Method for directional location and locating system

ABSTRACT

In order to locate electromagnetic or acoustic signal sources of a sensor configuration ( 1   a  through  1   c ) fitted with at least two electric outputs, where the incidence-dependent transfer functions between the acoustic signals incident on the input(s) of the sensor configuration ( 1   a  through  1   c ) and the electric output signals are different, the ratio ( 7   x  through  7   xx ) of the output signal is formed and the result then is correlated with the previously determined ratio function ( 11 ).

The insights leading to the present invention were acquired from theneeds relating to directionally locating acoustic signal sources.Accordingly the present description of the invention mostly concernsdirectionally locating acoustic sources. Nonetheless the expert easilyunderstands that this invention is immediately applicable also tolocating electromagnetic signal sources. The problem of ascertainingwhich kind the sources are being located only affects the kinds ofsensors used in this invention. In the special case of locating acousticsignals, the sensor configuration is a set of microphones whereas whenlocating electromagnetic sources the system consists of a set ofantennas followed by antenna amplifiers.

Presently procedures are known, which are mathematically complex ordemand substantial equipment in order to locate such sources, especiallyin a field of several sources. If now less equipment is used by reducingthe number of sensors, the mathematical complexity relating tosource-location discrimination will increase. When locating acousticsignal sources, illustratively the determination of phase differencesbetween acoustic signals simultaneously incident on the microphones ofthe microphone configuration will be selected.

The objective of the present invention is to propose a directionallocation method and a corresponding system whereby the cited costs canbe drastically reduced.

When using a sensor configuration of at least two electric outputs, anddifferent transfer functions—in the form of receiving lobes regardingthe dependence of the electric output signals on the direction ofincidence of the input signals—are effective between the electromagneticor acoustic input and the aforementioned at least two electric outputs,then it was observed that by taking the ratio of signals representingthe said output signals, a ratio function is formed which is unambiguousrelative to the angular position of a source and which is independent ofthe signal level. In this manner the proposed method unambiguouslydetermines an angular position at minimum design complexity and thismethod is basic in ascertaining two angular positions per source and tospatially unambiguously determine the source position in the sense of alocated beam and/or, in the case of simultaneously active sources, tolocate said sources at least within the scope of said cited one angularposition. As shall be elucidated farther below, when locating the sourceposition, a position cone results from the cited ratio, the apertureangle of said cone being used as position coordinate.

The unambiguous directional position of a source, that is, the locationof a local source beam, is possible in a preferred implementation of theinvention by analyzing at least three of the cited ratios, and for thatpurpose at least three electric outputs are provided each of which isassociated with a different transfer function of the above stated kind,that is having different receiving characteristics.

When the method discussed so far is used in an environment holding asingle, active signal source, then said source's position shall bedetermined. If on the other hand several sources are simultaneouslyactive, a spectrum of angular positions results and a single measurementdoes not immediately reveal how many sources are active at a particulardirectional location.

For that purpose a further preferred implementation of the inventionproposes carrying out the said generation of ratios several times intime-staggered manner and creating a histogram function from the ratiosand correlating said histogram function with the previously determinedratios/incidences dependences and to ascertain therefrom the directionalposition of at least one source.

This procedure is used preferably both when implementing the method ofthe invention using two of the cited outputs as well as theimplementation using three outputs.

In the proposed histogram function, electromagnetic or acoustic signalsfrom sources that have been active for some extended time will result inequal ratios and this phenomenon leads to accumulating these values inthe attained histogram function. When correlated with the dependence ofratio and incidence that was determined beforehand, said accumulatingvalues lead directly to ascertaining the particular at least one angularposition of the signal sources active in the field.

In another preferred implementing mode, the output signals from theabove mentioned sensor configurations are analyzed in the frequencydomain. Considering that the cited transfer characteristics change onlywithin the rolloff range, then it follows that the effect of thefrequency will be eliminated when forming the ratio, especially so whenthe selected transfer characteristics all have the same rolloffbehavior. Therefore signal analysis in the frequency domain not onlymakes it possible to set up the said histogram from time-staggeredmeasurements, but also from the spectrum ratios simultaneouslyascertained in the frequency domain.

Preferably the transfer characteristics associated with the particularoutputs are selected so that they differ merely by a solid-angle phaseshift, i.e. that they “look” in a different direction but otherwise areidentical.

The method of the invention and the system of the invention areespecially well suited in locating acoustic sources and, because of thesimple equipment and low need for computation, they are especiallyapplicable to hearing aids.

The invention is elucidated in illustrative manner below and in relationto the attached drawings.

FIGS. 1a, 1 b show preferred transfer characteristics used in theinvention to locate acoustic sources for two sub microphoneconfigurations used in the minimum design,

FIG. 1c shows the common spatial orientation of the transfercharacteristics of the sub microphone configuration of FIGS. 1a and 1 b,

FIG. 2 shows the particular transfer characteristic and the ratio overone of the solid angles φ of FIGS. 1a and 1 b,

FIG. 3 shows the ratio of FIG. 2 as a function of the solid angle φ toelucidate the correlation of the actual measurement and pre-knowndependence between ratio and angle φ,

FIG. 4 shows an illustrative histogram derived from time-staggeredascertained ratios,

FIG. 5 is a simplified signal-flow/functional block diagram of aposition-locating system designed in the manner of the invention andoperating on the basis of the method of the invention, used withacoustic sources and in a preferred embodiment mode,

FIG. 6a shows the position of a signal source determined by the methodor the system of the invention in its minimum design,

FIG. 6b shows two locating beams ascertained in a further development ofthe invention, and

FIG. 6c shows the determination of a locating beam determined in afurther preferred embodiment of the invention.

The method of the invention is outlined in FIGS. 1 through 4 withoutclaim to scientific rigor using simple transfer characteristics eachcorresponding to first-order cardioids. By means of this simpleprocedure described below in easily followed manner, the expert willunderstand how one or more acoustic sources can be located in the mannerof the invention using fairly complex transfer functions.

A first sub microphone circuit—which broadly is called the sensorconfiguration—of a microphone or sensor configuration is assumed beingfitted with the 3D transfer function shown in 2D in FIG. 1a having thetransfer/amplification characteristic of a signal incident on it in thedirection φ.

In a view similar to FIG. 1a, FIG. 1b shows a second sensorconfiguration's transfer function which is assumed the mirror imagerelative to the axis π/2; 3π/2 to the first sensor array. The transferfunction of FIG. 1a is denoted by c_(N) and that of FIG. 1b by c_(Z).FIG. 1c simultaneously shows the transfer functions c_(N) and c_(Z) asthey are present in a sensor array with corresponding sub sensorcircuits and two electric outputs. As already mentioned, the location isthat of acoustic sources and the systems are microphone configurations.

FIG. 2 shows the values in dB of the transfer functions c_(N) or c_(Z)depending on the φ axis of FIGS. 1a-1 c.

If unit signals are incident on the two sub sensor arrays, the transferfunctions shown in FIGS. 1a and 1 b simultaneously correspond to theparticular signal values at the outputs of the sensor configurationsbeing considered. In the invention, the ratio is then formed from thesetwo output signals which also are denoted by c_(N) and c_(Z), namely

Q=/c _(N) /÷/c _(Z)/.

The function Q is qualitatively shown in FIG. 2 in dashed lines with apole at φ=π. In FIG. 3 the function Q(φ) is again plotted between φ=0and φ=π.

Be it borne in mind that when forming the ratio Q, which for clarity wasinitially discussed for unit signals, the particular values of the inputsignals cancel out and that as a result the angular dependence shown inFIG. 3 applies to arbitrary signals incident at an angle φ on the sensorarray.

When such a function is measured and stored and, as shown in FIG. 3, theinstantaneous ratio Q_(INS) is formed from an instantaneously incidentsignal INS, and is rendered again in dB, then this dB value can becorrelated with the stored ratio function Q(φ), that is, it can beentered into the previously stored function/dependence Q(φ): thedirectional position φ_(ins) of the instantaneously incident acousticsignal is determined.

As can be inferred from FIG. 3 and as is anyway obvious from FIGS. 1aand 1 b, the ratio function Q(φ) is unambiguous from 0 to 180°, thoughonly in the 2D sectional plane through the transmission lobes shown inFIGS. 1a and 1 b. A positional angle φ is determined which correspondsto a position cone shown in dashed lines in FIG. 1a for the apertureangle φ0 shown therein.

If location must be determined unambiguously, at least three of theabove cited sub sensor circuits must be used and correspondingly onesensor configuration with three outputs. Derivation of the ratio in themanner described above and the correlation with the particularpre-recorded dependences Q(φ) are carried out pairwise on two,preferably three circuit output signals.

Even though the position information ascertained so far reveals that anacoustic signal was determined from the cited directional positionwhether for two sub sensor circuits corresponding to one position coneor spatially for more than two sensor configurations by means of two orone position beams, nor more is known than that instantaneously anacoustic signal is incident from the cited direction. Accordingly alocated signal source is instantaneously active.

However in order to obtain information on the position of a sourceactive over a substantial time interval in distinction fromstochastically distributed acoustic signals incident form differentdirections, basically the observation runs over the time interval aboutwhich directional position contains an accumulation of signals with theconclusion that an acoustic signal source is located there.

For that purpose the cited ratio Q_(INS) is derived again from theoutput signals so that, as illustratively shown in FIG. 4, a histogrammay be drawn up. Accordingly the frequencies are recorded (in dBaccording to FIG. 4) in ratio-value specific manner. FIG. 4 shows anillustrative recorded histogram with a frequency n of ratio values thatoccurred. The inference is that, according to the accumulation, anacoustic signal source is active at about−38 dB and at−20 dB accordingto FIG. 3 in the direction φ≈15° and another at φ≈35°.

The proposed method is usually appropriate for execution in thefrequency domain. If it be taken into consideration that the transferfunctions such as shown in FIGS. 1a and 1 b because of frequency rolloffeach change in frequency in similar manner, then it follows that thecited ratio function becomes frequency independent. Thereby the sensorconfiguration's output signals may be converted consecutively severaltimes into the frequency domain and said ratio derivation—which containsthe same directional information independently of frequency—can becarried out for a selected number of amplitudes in the frequencyspectrum.

Using a number N of sub sensor circuits, in particular microphoneconfigurations, the proposed method makes it possible to locate, apossibly substantially larger number M of especially acoustic signalsources. If more than two sub sensor configurations are used, it will befeasible to unambiguously carry out spatial location. Furthermore andillustratively, the distribution shown in FIG. 4 shows that in angularposition range of 110 to 130°, two or more possible identical sourcesare highly likely to be active.

FIG. 5 is a simplified signal-flow/functional block diagram of apositioning system operating by the method of the invention andillustratively shown for acoustic signals. It is especially well suitedfor a hearing aid.

The system of the invention comprises a microphone configuration 1comprising at least two sub-microphones 1 _(x) as shown with threesub-microphone circuits 1 b-1 c running to corresponding outputs A_(1a)through A_(1c). The three sub-microphone circuits are of differenttransfer functions, for instance being first-order cardioids pointing indifferent directions, such a design illustratively and preferably beingimplemented by the sub-microphone circuits being two microphones ofwhich the outputs are linked to each other in the “delay and add”manner. Using three sub-microphone circuits implements a third cardioidin turn making it possible—as elucidated farther below—to derivesimultaneously two or three ratios. In this manner two position conesare implemented as shown in FIG. 6b or three as shown in FIG. 6c. Whenthere are two position cones, a source still is ambiguous, whereas whenthere are three it shall be located unambiguously.

In a preferred embodiment, the output signals A_(xy) are converted intothe frequency domain at time/frequency transducer units FFT 3 a-3 c. Theoutputs of the time/frequency transducer units 3 a-3 c are operationallyand pairwise connected as shown each through value-forming units withdenominator or nominator inputs of three ratio-forming units 7 _(I),through 7 _(III). The outputs of the ratio-forming units 7 _(I) through7 _(III) are operationally connected to an analyzer 9 where, as alreadydiscussed, in particular the histograms will be formed. In order toimplement the correlation of the determined ratio-value distributionswith the ratio/angular-position dependence, and as schematically shownin FIG. 5, the functions Q(φ₁) through Q(φ₃) are fed to the analyzer 9.These functions were measured/computed beforehand using the sensorconfiguration 1 if present and are shown in schematic manner stored inthe function memory 11. The symbols φ₁ through φ₃ denote the apertureangle of the position cone of FIGS. 6a through 6 c. Performing anappropriate conversion in the analyzer 9, that is analyzing thehistogram distribution and associating its peak values to thecorresponding position angles φ₁ through φ₃, then recalculatingappropriately depending on the desired position coordinates, the outputof the analyzer 9 will display the number M of detected acoustic sourcestogether with their angular positions.

The proposed method of the invention is unusually well suited to hearingaids and may be used to point the directional characteristics of ahearing aid toward detected sources or—if such sources were defined orknown to be spurious—to introduce high attenuation in said locateddirection.

Basically all known or microphone /sensors and their combinations may beused as sub microphone circuits/sub sensor circuits, said circuits beingfitted with different transfer functions as required in the operationalposition and as required regarding acoustic signals incident at an angleφ.

However the invention proposes, especially for simple and easilymonitored implementation, that identical sub sensor circuits be used ofwhich the transfer functions while being identical on the other handwith respect to their axial alignment (corresponding to φ=0) in FIG. 1a)shall be directed differently spatially.

The method of the invention makes it possible—without determining signalphases/signal time delays and without using corresponding laborious logtaking of complex variables—to locate in exceedingly simple mannersignal sources in the surroundings—by forming ratios and then byanalysis—in particular with respect to acoustic sources in an acousticfield.

What is claimed is:
 1. A method for directionally locating at least oneelectromagnetic or acoustic signal source comprising the steps of:providing a sensor configuration consisting of exactly two outputs, saidsensor configuration having transfer functions between an input on whichsaid electromagnetic or acoustic signals impinge and said two outputs togenerate signals on the outputs that are differently dependent on thespatial angle with which said electromagnetic or acoustic signalsimpinge on said input, said spatial angle thereby defining a locus of aspatial cone about a spatial axis whereon said source is situated;defining a predetermined course of a ratio of said signals generated atsaid two outputs in dependency of said spatial angle; monitoring a ratioof momentarily prevailing signals at said two outputs; and determiningsaid spatial angle defining said locus of a source generating saidmomentarily prevailing signals, said determining including correlatingsaid ratio of momentarily prevailing signals compared with saidpredetermined course of said ratio.
 2. The method of claim 1, furthercomprising the step of monitoring said ratio repetitively and forming ahistogram from a signal which is dependent on said ratio as monitoredrepetitively, and performing said determining as a function of saidhistogram.
 3. The method of claim 2, wherein multiple sources can bedetected and directionally located by said method.
 4. The method ofclaim 1, further comprising the step of performing a time-domain tofrequency-domain conversion on said momentarily prevailing signals. 5.The method of claim 1, further comprising the step of tailoring saidtransfer functions to be substantially of equal shape but phase-shiftedby a predetermined spatial angle.
 6. The method of claim 1, furthercomprising the step of assuming a directional hemisphere of infiniteradius wherein said source must lie.
 7. A method for directionallylocating at least one electromagnetic or acoustic signal source relatedto a sensor configuration which has at least two electric outputs, saidsensor configuration having transfer functions between an input on whichsaid electromagnetic or acoustic signals impinge and said two outputs togenerate electric signals on the outputs that are differently dependenton the spatial angle with which said electromagnetic or acoustic signalsimpinge on said input, said spatial angle thereby defining a locus of aspatial cone about a spatial axis whereon said source is situatedcomprising the steps of: defining a predetermined course of a ratio ofsaid electric signals generated at two of said at least two outputs independency of said spatial angle; monitoring a ratio of momentarilyprevailing electric signals at said two outputs; and determining saidspatial angle defining said locus of a source generating saidmomentarily prevailing electric signals, said determining includingcorrelating said monitored ratio of momentarily prevailing electricsignals with said predetermined course of said ratio.
 8. The method ofclaim 7, further comprising the steps of providing at least twice saidtwo electric outputs from at least two pairs of at least three of saidelectric outputs, thereby determining at least two of said spatialangles.
 9. The method of claim 8, providing three of said pairs anddetermining three of said spatial angles.
 10. The method of claim 7,further comprising monitoring said ratio repetitively and forming ahistogram from a signal which is dependent on said ratio as monitoredrepetitively, and performing said determining as a function of saidhistogram.
 11. The method of claim 10, wherein multiple sources can bedetected and directionally located by said method.
 12. The method ofclaim 7, further comprising the step of performing a time-domain tofrequency-domain conversion on said momentarily prevailing signals. 13.The method of claim 7, further comprising the step of tailoring saidtransfer functions to be substantially of equal shape but phase-shiftedby a predetermined spatial angle.
 14. The method of claim 7, furthercomprising the step of assuming a directional hemisphere of infiniteradius wherein said source must lie.
 15. A system for directionallylocating at least one source of electromagnetic or acoustical signalscomprising: a sensor configuration with at least two electric outputs,the sensor configuration having transfer functions between an input onwhich said electromagnetic or acoustic signals impinge and said twooutputs to generate electric signals on the outputs that are differentlydependent on the spatial angle with which said electromagnetic oracoustic signals impinge on said input, wherein two of said at least twoelectric outputs are operationally connected to a ratio forming unit,the output of said ratio forming unit being operationally connected toan input of an analyzer unit, the analyzer unit generating in dependencyof an output signal of said ratio forming unit an output signal which isindicative of a locus whereon said source is situated defined as aspatial cone with an opening angle according to said spatial angle. 16.The system of claim 15, further comprising at least twice said twoelectric outputs, said analyzing unit generating an output signalrepresentative of at most two intersections in space of at least two ofsaid loci whereupon said source is situated.
 17. The system of claim 15,further comprising time to frequency conversion units interconnectedbetween said electric outputs and said input of said analyzing unit. 18.The system of claim 15, further comprising means for forming a histogramfrom said outputs of said ratio forming unit and said output of saidanalyzing unit.
 19. The system of claim 15, wherein said sensorconfiguration is formed by a microphone configuration of a hearingdevice and wherein said ratio forming unit and said analyzing unit arewithin said hearing device.
 20. The system of claim 19, wherein meansfor forming a histogram is provided between the output of said ratioforming unit and the output of said analyzing unit for increasingaccuracy of detecting said locus in a acoustically noisy environmentwith said source.
 21. The method of claim 20, wherein multiple sourcescan be detected and directionally located by said system.
 22. A methodfor directionally locating at least one electromagnetic or acousticsignal source comprising: a sensor configuration which has at least twoelectric outputs, said sensor configuration having transfer functionsbetween an input on which said electromagnetic or acoustic signalsimpinge and said two outputs to generate electric signals on the outputsthat are differently dependent on the spatial angle with which saidelectromagnetic or acoustic signals impinge on said input, said spatialangle thereby defining a locus of a spatial cone about a spatial axiswhereon said source is situated; means for defining a predeterminedcourse of a ratio of said electric signals generated at two of said atleast two outputs in dependency of said spatial angle; means formonitoring said ratio of momentarily prevailing electric signals at saidtwo outputs; and means for determining said spatial angle defining saidlocus of a source generating said momentarily prevailing electricsignals, said determining including correlating said monitored ratio ofmomentarily prevailing electric signals with said predetermined courseof said ratio.
 23. The system of claim 22, further comprising a meansfor monitoring said ratio repetitively and a means for forming ahistogram from a signal which is dependent on said ratio as monitoredrepetitively, and performing said determining as a function of saidhistogram.
 24. The system of claim 22, wherein multiple sources can bedetected and directionally located by said system.
 25. The system ofclaim 22, further comprising a means for performing a time-domain tofrequency-domain conversion on said momentarily prevailing signals. 26.The system of claim 22, wherein said sensor configuration consists ofexactly two electric outputs.
 27. The system of claim 22, wherein adirectional hemisphere of infinite radius wherein said source must lieis assumed.